The present invention relates to an object extracting method of extracting a position of an object in a specified region to be inspected through image processing.
During the manufacturing process of various kinds of products such as semiconductor wafers, etc., the position where an object on the surface of the product is present is often extracted in a manner of an image processing in order to read out an indicia, for example, a symbol or the like assigned to the product. The position of a defect, etc. on the surface of the product is also extracted in many cases through an image processing.
In such cases as above, the light is projected to the surface to be inspected, thereby to obtain the density value at each position of the surface through an image processing.
The density value for each position is integrated and then projected on the X and Y axes. In other words, the density value at each position along the Y axis is integrated and then projected onto the X axis, and the density value at each position along the X axis is integrated and then projected onto the Y axis. FIG. 7 is a diagram showing an example of density values expressed by using any of 0-7 in 8 gray scale on a specified region 1 shown in FIG. 1(a) and projected density values based on the density values in the conventional method. More concretely, supposing that the density values at each of ten points on the Y axis in the Y coordinate (y.sub.1) are the levels (1, 3, 2, 4, 5, 6, 4, 1, 2, 1), the integrated result of the levels is 29 and then projected as the coordinate value on the Y axis (.SIGMA.(y.sub.1)=29). On the other hand, if the density values at each of the ten points on the Y axis in the next Y coordinate (y.sub.2 ) are the levels ( 1, 1, 2, 2, 1, 3, 1, 3, 2, 1), the integrated sum 17 is projected as the coordinate value on the Y axis (.SIGMA.(y.sub.2)=17). The above procedure is repeated not only for the Y axis, but for the X axis, whereby a projection graph as shown in FIG. 9 is obtained on the image. In the drawing, reference numeral 1 is a specified region, i.e. a surface to be inspected and 2.sub.1, 2.sub.2, 2.sub.3 are objects (symbols A, B, C) to be extracted. In the example of FIG. 9, dotted lines show the result of the conventional method while solid lines show the result of the present invention described later. In FIG. 9, since the density of the object 2 is higher than that of the ground of the surface 1, a section including XY coordinate regions R.sub.x1, R.sub.x2, R.sub.x3, R.sub.y where the level of the integrated density value is high is determined and extracted as the existing place of the object 2.
In the above-described method, if the object has a small contrast, the position of the object 2 cannot be extracted or erroneously detected due to the influence of noise present in the to-be-inspected surface 1, i.e., the influence of the change of the density not resulting from the existence of the object. That is, erroneous recognition is caused. More specifically, in the foregoing example, although the density value at all points where the object 2 is not present is supposed to be the level 1, there may appear and be included in the integrated sum the density value of a higher level (level 2 or 3) due to the noise. In consequence, the integrated value .SIGMA.(y.sub.2 ) of the density value at the Y coordinate y.sub.2 is not ten times the level 1, but becomes 15 because of the inclusion of the high-level density value (level 2 and level 3). Therefore, while the integrated value .SIGMA.(y.sub.1) of the density value at a point y.sub.1 on the Y coordinate where the object 2 is present is 29, the integrated value .SIGMA.(y.sub.2) of the density value at a point y.sub.2 on the Y coordinate where the object 2 is not present becomes 15. Since the difference of the integrated values is as small as 14, it results erroneous recognition.